Explanation

(b)
In a double bond $(\ = \ )\$one$\ \sigma\$and$\$on$e\ \pi$-bond is present while in a single bond $(\ - \ )$ only $\sigma$-bond is present.
The structure of the naphthalene is as
[image:4_image102.emf]
In naphthalene five double bonds are present, hence $5\pi$ bonds are present in naphthalene.